1. Field of the Invention
The present invention relates to improvements in long range fixed site wide aperture direction finding systems, and more particularly pertains to systems with circular arrays of receiving antennas. These arrays usually consist of two rings of antennas with reflector screens which provide a single ended pattern. A wide aperture direction finder (WADF) is one in which the arriving wavefront is sampled simultaneously by an array of antennas extending over a distance of one wavelength or greater, as opposed to an Adcock type which has apertures of a few tenths of a wavelength.
2. Prior Art
In the field of WADF's it has been the general practice to use narrow lobes and high rotation rates. This puts severe limitations on the receiving system and the bandpass of the IF and detecting circuitry, and in some cases even requires a dual receiving system. The antennas are usually fed through delay lines to the combiner networks to simulate a broadside pickup pattern with a portion of the circular array. A goniometer spinning at a constant rate couples the antenna signal to a coaxial feed to the receiving system. The most common, Wullenweber WADF's employ circular rings of identical elements requiring huge reflector screens. These circular ring arrays are quite costly to construct and maintain while achieving satisfactory radiation patterns over only about 3:1 or 4:1 frequency range. In most cases at least two ring arrays are required to give even the most minimal coverage over the 15:1 frequency range from 2 to 30 MHz. Ionospheric disturbances such as multipath propagation characteristically generate substantial bearing errors in the HF spectrum which are difficult to resolve with conventional single lobe methods.